added a helper function to parse human readable deterministic paths

Simple helper function that allows to do the following:

    List<ChildNumber> path = HDUtils.parsePath("44' / 0' / 0' / 1 / 1");

instead of

    List<ChildNumber> path = ImmutableList.of(new ChildNumber(44, true), new ChildNumber(0, true),
        new ChildNumber(0, true), new ChildNumber(1, false), new ChildNumber(1, false));
You may as well return the list without making it immutable. It'll be owned by the caller anyway, there's no additional safety to be gained by freezing it.